Police investigating the death of oil executive Carole Waugh have arrested a woman on suspicion of conspiracy to defraud.
Miss Waugh, originally from Durham but living in London, had not been seen by her family since mid-April.
Her body was found with a single stab wound inside a car at a garage in Lime Court, New Malden, south-west London, on August 2.
Scotland Yard said a 61-year-old woman was arrested on Friday and was being held in custody at a south London police station.
Ms Waugh was reported missing by her family on May 7. They last saw her at a family party in mid-April. She had lived and worked in Libya for a number of years, but returned to London in 2008 and would regularly visit relatives in Durham and Cumbria.
Her former boss, Stuart Anderson, told journalists she had fled Libya after being threatened by someone in Colonel Muammar Gaddafi's regime, but a Scotland Yard spokesman said inquiries were focused in London.
Detectives said she met men through a variety of internet sites, including dating websites, and they were investigating the possibility that she might have been an escort.
So far, a total of 11 people have been arrested in connection with the inquiry into Miss Waugh's disappearance. At least three women have tried to pose as her since she vanished, police said. Her flat is in an affluent part of central London and her brother Chris previously said she was "very frugal" with money.
A second man was arrested on suspicion of murder on Thursday and is still being questioned by police. Rakesh Bhayani, 40, of Chamberlayne Avenue, Wembley, also faces three charges of conspiracy to commit fraud by false representation worth about £280,000, following transactions associated with Ms Waugh's identity and is due in court next month in connection with those.
The other man, Nicholas David Kutner, 47, of no fixed abode, was arrested on suspicion of murder and kidnap last week. He also faces two charges relating to renting her property at Tressard Court and a fourth of unlawfully withdrawing funds from the 50-year-old's bank account. Kutner is also facing a fraud charge after being accused of pretending to be Chris Waugh, Ms Waugh's brother, in a bid to sell her London home.